1. Field of the Invention
This invention relates to illumination devices and systems as well as related functions and components, and in particular, it relates to illumination devices and systems useful in stage lighting.
2. Description of the Related Art
Current high power stage lights use metal halide discharge lamps as the light source. Because such lamps are white light sources, color lights of various colors are obtained by using color filters in front of the metal halide discharge lamps. Metal halide discharge lamps have relatively short life, typically from a few hundred to a few thousand hours. When color filters are used to obtain light of various colors for stage lighting, the color lights have relatively low color saturation, and their colors are neither very vivid nor very rich. LED (light emitting diodes) light sources are clean and energy efficient light sources and have long life. With the achievable luminous flux of LED light sources increasing every year, LED light sources are becoming more widely adopted as illumination devices. As LEDs can emit monochromatic lights of various colors, using LED light sources for stage lighting can achieve color lights without using filters. Further, by adjusting the drive current of LEDs of various base colors such as primary colors red, green and blue, desired colors of the output light can be achieved. The relatively high saturation of monochromatic LED light sources offers more freedom in generating desired color lights for stage lighting systems.
Current LED light sources tend to generate a large amount of heat which limits the output power of individual LED chips, and their light emitting efficiency is still relatively low. Thus, high power stage lighting systems use LED arrays to achieve the desired luminous flux.
Chinese patent application No. 200720061982.0 describes a light source system for stage lighting, which employs a LED array and a large heat dissipation device to provide a power of 100 W. This system can also achieve adjustable color by controlling the power of the LEDs of different colors in the LED array. However, due to concerns on heat dissipation and luminous flux, as well as uniformity of brightness and color of the output light, this system still cannot satisfy the need for high power stage lighting systems.
To overcome the problems of the above system, an improved system is described in a Chinese patent application filed by the applicant of this application. This system employs a wavelength-based light combining device to combine monochromatic lights from multiple LED arrays into one light beam. This system offers increased output power and improved uniformity of brightness and color of the output light.
The above systems have certain shortcomings.
1. The individual LED chips in the LED array have different emission spectra, brightness and temperature characteristics. When the light from the multiple LED chips are combined by downstream optical elements and projected on a stage or on a screen, various parts of the stage or screen corresponding to the different LED chips may have different brightness and color spectrum, causing the local color cast in the projected image.
2. The light combining device used in the above systems does not provide ideal light combining result in combining the multiple monochromatic lights, so that the projected image on the stage or screen has inferior color uniformity, in particular when white color is output.